ATOMIC STRUCTURE & NUCLEAR ANS
1. 1s2 2s22p6 3s23p3 Atoms of an element, X, have the electronic configuration shown
above. The compound most likely formed with magnesium, Mg, is
(A) MgX
(B) Mg2X
(C) MgX2
(D) MgX3
(E) Mg3X2
E
2. The elements in which of the following have most nearly the same atomic radius?
(A) Be, B, C, N
(B) Ne, Ar, Kr, Xe
(C) Mg, Ca, Sr, Ba
(D) C, P, Se, I
(E) Cr, Mn, Fe, Co
E
3. Which of the following represents the ground state electron configuration for the Mn3+
ion? (Atomic number Mn = 25)
(A) 1s2 2s22p6 3s23p63d4
(B) 1s2 2s22p6 3s23p63d5 4s2
(C) 1s2 2s22p6 3s23p63d2 4s2
(D) 1s2 2s22p6 3s23p63d8 4s2
(E) 1s2 2s22p6 3s23p63d3 4s1
A
4. Ca, V, Co, Zn, As
Gaseous atoms of which of the elements above are paramagnetic?
(A) Ca and As only
(B) Zn and As only
(C) Ca, V, and Co only
(D) V, Co, and As only
(E) V, Co, and Zn only
D
5. One of the outermost electrons in a strontium atom in the ground state can be described
by which of the following sets of four quantum numbers?
(A) 5, 2, 0, 1/2
(B) 5, 1, 1, 1/2
(C) 5, 1, 0, 1/2
(D) 5, 0, 1, 1/2
(E) 5, 0, 0, ½
E
Use the following answers for questions 6-8
(A) F
(B) S
(C) Mg
(D) Ar
(E) Mn
6. Forms monatomic ions with 2¯ charge in solutions
7. Forms a compound having the formula KXO4
8. Forms oxides that are common air pollutants and that yield acidic solution in water
B, E, B
Use these answers for questions 9-11
(A) O
(B) La
(C) Rb
(D) Mg
(E) N
9. What is the most electronegative element of the above?
10. Which element exhibits the greatest number of different oxidation states?
11. Which of the elements above has the smallest ionic radius for its most commonly found
ion?
A, E, D
12. Which of the following conclusions can be drawn from J. J. Thomson's cathode ray
experiments?
(A) Atoms contain electrons.
(B) Practically all the mass of an atom is contained in its nucleus.
(C) Atoms contain protons, neutrons, and electrons.
(D) Atoms have a positively charged nucleus surrounded by an electron cloud.
(E) No two electrons in one atom can have the same four quantum numbers.
A
Use these answers for questions 13-16
(A) 1s2 2s22p5 3s23p5
(B) 1s2 2s22p6 3s23p6
(C) 1s2 2s22p62d10 3s23p6
(D) 1s2 2s22p6 3s23p63d5
(E) 1s2 2s22p6 3s23p63d3 4s2
13. An impossible electronic configuration
14. The ground-state configuration for the atoms of a transition element
15. The ground-state configuration of a negative ion of a halogen
16. The ground-state configuration of a common ion of an alkaline earth element
C, E, B, B
Questions 17-20
(A) Heisenberg uncertainty principle
(B) Pauli exclusion principle
(C) Hund's rule (principle of maximum multiplicity)
(D) Shielding effect
(E) Wave nature of matter
17. Can be used to predict that a gaseous carbon atom in its ground state is paramagnetic
18. Explains the experimental phenomenon of electron diffraction
19. Indicates that an atomic orbital can hold no more than two electrons
20. Predicts that it is impossible to determine simultaneously the exact position and the exact
velocity of an electron
C, E, B, A
21. Which of the following sets of quantum numbers (n, l, ml, ms) best describes the valence
electron of highest energy in a ground-state gallium atom (atomic number 31) ?
(A) 4, 0, 0, 1/2
(B) 4, 0, 1, 1/2
(C) 4, 1, 1, 1/2
(D) 4, 1, 2, 1/2
(E) 4, 2, 0, ½
C
22. All of the following statements concerning the characteristics of the halogens are true
EXCEPT:
(A) The first ionization energies (potentials) decrease as the atomic numbers of the
halogens increase.
(B) Fluorine is the best oxidizing agent.
(C) Fluorine atoms have the smallest radii.
(D) Iodine liberates free bromine from a solution of bromide ion.
(E) Fluorine is the most electronegative of the halogens.
D
Question 23-26 refer to atoms for which the occupied atomic orbitals
shown below.
23. Represents an atom that is chemically unreactive
24. Represents an atom in an excited state
25. Represents an atom that has four valence electrons.
26. Represents an atom of a transition metal.
D, A, C, E
27. In the periodic table, as the atomic number increases from 11 to 17, what happens to
the atomic radius?
(A) It remains constant.
(B) It increases only.
(C) It increases, then decreases.
(D) It decreases only.
(E) It decreases, then increases.
D
28. Which of the following is a correct interpretation of the results of Rutherford's
experiments in which gold atoms were bombarded with alpha particles?
(A) Atoms have equal numbers of positive and negative charges.
(B) Electrons in atoms are arranged in shells.
(C) Neutrons are at the center of an atom.
(D) Neutrons and protons in atoms have nearly equal mass.
(E) The positive charge of an atom is concentrated in a small region.
E
29. The ionization energies for element X are listed in the table above. On the basis of
the data, element X is most likely to be
(A) Na
(B) Mg
(C) AI
(D) Si
(E) P
C
30. For the types of radiation given, which of the following is the correct order of
increasing ability to penetrate a piece of lead?
(A) Alpha particles < gamma rays < beta particles
(B) Alpha particles < beta particles < gamma rays
(C) Beta particles < alpha particles < gamma rays
(D) Beta particles < gamma rays < alpha particles
(E) Gamma rays < alpha particles < beta particles
B
1980 D
Answer:
(a) 1s2 2s22p6 3s23p63d10 4s24p3 or
[Ar] 3d10 4s24p3
n l ml ms
(b)
4 0 0  12
n
l
ml
ms
4
0
0
-½ opposite spin for s electrons
4
0
0
+½
4
1
-1
-½
4
1
0
-½ opposite spin for p electrons
4
1
+1
-½
consistent set of n, l, ml values
(c) Paramagnetic. There are 3 unpaired 4p electrons.
(d) An As atom can accept 3e- from electropositive Na atoms to give As atom a pseudoKr electron configuration. Ionic Na3As results.
An As atom share 3e- for a share of an electron from each of 3 Cl atoms to get
pseudo-Kr configuration for As atom in covalent AsCl3.
An As atom can share all 5 valence electrons by using 4d - as well as 4s and 4porbitals (either through M.O.’s or L.C.A.O. hybrids) to give covalent AsF5.
1990
Answer:
(a) Across the period from Li to Ne, the number of protons is increasing in the nucleus.
Hence, the nuclear charge is increasing with a consequently stronger attraction for
electrons and an increase in ionization energy.
(b) The electron ionized in the case of Be is a 2s electron, whereas, in the case of B it is
a 2p electron. 2p electrons are higher in energy than 2s electrons because 2p
electrons penetrate to the core to a lesser degree.
(c) The electron ionized in O is paired with another electron in the same orbital, whereas
in N the electron comes from a singly-occupied orbital. The ionization energy of the
O electron is less because of the repulsion between the two electrons in the same
orbital.
(d) The ionization energy of Na will be less than those of both Li and Ne because the
electron removed comes from an orbital that is farther from the nucleus and,
therefore, is less tightly held.
2007 Q # 2
(a) (i) let X = decimal percentage of Ne-20, then (1-X) = decimal percentage of Ne-22
19.99X + 21.99(1-X) = 20.18; X = 0.905 or 90.50% Ne-20 and 9.500% Ne-22
(ii) (12.55 g)(9.5%) 

1 mol Ne 6.02  10 23 atoms
= 3.5571022 atoms

20.18 g
1 mol
3.0  10 8 m s-1 10 9 nm

(b) c = ;  = 
= 690 nm
c 4.34  1014 s-1
1m
2007 part B, form B, question #6
Answer:
(a) element 2, the more metallic an element, the easier it is to remove an electron and the
lower its first ionization energy
(b) magnesium; electron configuration is 1s2 2s2 2p6 3s2; it is in the 3 period of the table
and has 2 valence electrons (the 3s2)which can be relatively easily removed (as shown
by a moderately low first and second ionization energy), the third ionization energy is
very high indicating the removal of a core electron, a 2p.
(c) 1s2 2s2 2p6 3s2
(d) +1
(e) Na
(f) element 1
1985 D
Answer:
(a) Oxides at left are basic and become less basic / more acidic as one moves to the
right.
Basic oxide: Na2O + 2 H2O  2 Na+ + 2 OHor: MgO + H2O  Mg(OH)2
Acidic oxide: any one of the oxides of Cl, S, or P
SO2 + H2O  H2SO3 (or equivalent for another oxide)
(b) Oxidizing strengths of halogen elements decrease down the group. Since atoms get
larger down the group, the attraction for electrons decreases and oxidizing strength
decreases.
(c) Reducing strengths of alkali metals increases down the group. Since atoms get larger
down the group, loss of outer electrons is easier and reducing strength increases.